1. Field of the Invention
This invention relates to a device by means of which a cornea taken from a donated eye is held for processing; the cornea being placed on a round substrate having a central opening. The outer edge of the cornea is pressed against the substrate by an annular retaining means. A cavity between the substrate and the cornea is established by filling of a pressure medium which is introduced in the central bore to the cavity.
2. Description of the Prior Art
Disclosed in U.S. Pat. No. 4,077,411 is a device to hold cornea tissue while a trephine cut is made by boring through the cornea of a donated eye. The device comprises a plastic body having a convex surface on which the donated cornea is placed and pressed against the convex surface by an annular disc, using tension springs. A liquid cushion is provided between the cornea and the convex surface of the plastic body to prevent damage to the endothelium layer. The liquid cushion is formed by liquid supplied through a central bore in the plastic body. This device is designed exclusively for perforating keratoplasty and for removing lamellar grafts which are unsuitable for refractive surgery on the cornea, i.e. for changing refractive power of the cornea.
It is known in the art to transplant a cornea by using cornea tissue taken from a donated eye. A distinction is made in this art between perforating keratoplasty and lamellar keratoplasty. In perforating keratoplasty, a cornea disc to be transplanted is obtained by a vertical punching-out of the cornea such as can be obtained by trephine cut. The total thickness of cornea disc is the same as the thickness of the cornea. In lamellar keraloplasty, a horizontal cut across the cornea is made to obtain a layer of cornea which comprises the transplant used for altering the refractive power of the cornea.
In order to obtain a disc of cornea from the donate tissue, the slice of donated cornea is usually placed on a concave substrate so that the top surface of the cornea slice, i.e, the epithelium, confronts the substrate and the inner surface or endothelium is upward and exposed above. The disc of cornea for transplanting is pierced or punched out by using a trepan, i.e. a round knife. A similar disc is removed, likewise by trepanning, from the recipient, i.e., the patient. One disadvantage of the known method used for obtaining cornea discs by perforation, is that during the trepanning operation the donated cornea rests on a substrate which is hard or does not have variable elasticity, so that in the supported condition the cornea will inevitably be completely deformed from the contour of the cornea during the trepanning operation on the patient's eye. It is therefore impossible to obtain identical trepanned disc of cornea, as is necessary for optimum perforating keratoplasty. One reason is that the pressure of the eye varies from patient to patient and because every oblique trepanning operation results in an oval cut and consequently an oval recess in the cornea. Every change in pressure during the trepanning process inevitably results in a change in the diameter of the removed cornea disc. Differences in pressure when trepanning a patient's eye result in relatively severe buckling of the cornea disc in the inner curve of the trepan.
In the known device, where the epithelium of the donated cornea rests downwards on the substrate, differences in deformability result in differences of shape relative to the cornea tissue taken by trepanning from the patient's eye.
An apparatus is disclosed in U.S. patent application Ser. No. 712,249, filed Mar. 15, 1985, and the corresponding West German patent application DE 3409798 for holding a disc of cornea taken from a human eye. The apparatus comprises plunger like moldings which are interchangeably supported in a recess provided in a support member. The support surface of the molding is concave or convex with a predetermined curvature and gas pervious openings communicate with an evacuation chamber so that a corneal disc can be sucked against the corneal support surface by a negative pressure. A pressure ring engages the edge of the corneal disc for clamping it between the pressure ring and molding. A guideway for a transversely-movable cutting device is adjustable relative to the molding. The apparatus is not used for holding a cornea taken from a donated eye, but for holding a lamellar slice of cornea which is taken from the human eye for processing so as to alter the refractive power, using the fixing device, and finally the altered lamanar slice is inserted in the patient's cornea. In order to secure the slice of cornea for processing, its outer edge is bent about the edge of the surface of the bearing member and held by the inner edge of the thrust collar in the space between the collar and the molding member and against the wall of the molding member.